The present invention relates to a radio communication apparatus and a communication method, and more particularly to a radio communication apparatus and a communication method for forming a frame with a plurality of slots and inserting a guard interval into each slot along with data for a mobile station to perform communication.
An example of a radio communication system using a guard interval is an orthogonal frequency division multiplexing (OFDM) radio communication system. An OFDM radio communication system is a system which multiplies each of a plurality of orthogonal frequencies (sub-carriers) by a symbol (data), then performs inverse Fourier transform, and since the sub-carriers are orthogonal to one another on the frequency axis, a symbol can be individually acquired for each sub-carrier by performing Fourier transform at the receive side.
OFDM Transmitter
FIG. 13 is a block diagram depicting an OFDM transmitter in a conventional OFDM radio communication system. An encoding section 1 encodes high-speed binary data using convolutional encoder or turbo encoder, and a modulation section 2 modulates the encoded data after interleave, using M-bits modulation such as BPSK, QPSK or 16-QAM, for example. Then a serial/parallel converter (S/P converter) 3 converts the modulated data symbol into N symbols of parallel modulated data symbols, and generates N number of sub-carrier components.
N points of inverted fast Fourier transform section 4 performs inverted Fourier transform processing (IFFT) on N number of modulated signals (sub-carrier components), which are output from the S/P converter 3, and outputs N number of time signal components in parallel. A parallel/serial converter (P/S converter) 5 converts the N number of time signal components acquired by the IFFT processing into serial data, and outputs them as an OFDM symbol. A guard interval insertion section 6 inserts a guard interval GI into this OFDM symbol, a digital/analog converter (D/A) converts the output signal from the guard interval insertion section into an analog signal, and a radio section 8 up-converts the frequency of the base band signal into a radio signal, then amplifies and transmits the radio signal into a space by an antenna 9. In the following description, a case of using fast Fourier transform FFT and inverted fast Fourier transform IFFT are used for Fourier transform and inverted Fourier transform will be described, but discrete Fourier transform DFT and inverted discrete Fourier transform IDFT may be used.
FIG. 14 is a diagram depicting a guard interval insertion. A guard interval insertion means that the end part of the OFDM symbol is copied and added to the beginning thereof. By inserting a guard interval GI, the influence of inter-signal interference ISI caused by multi-paths can be eliminated.
OFDM Receiver
FIG. 15 is a block diagram depicting an OFDM receiver in the OFDM radio communication system. A band pass filter (BPF) 11 performs filtering on a signal received by an antenna 10 to remove an unnecessary frequency component, a down-converter (D/C) 12 converts the frequency of a radio signal into a base band frequency, an analog/digital converter (not illustrated) converts the analog of the base band signal into digital, and a guard interval removal section 13 removes the guard interval. An S/P converter 14 converts a time signal, after the guard interval is removed, into N number of parallel data, and inputs the data to N points of the Fourier transform section 15. The Fourier transform section 15 performs N points of FFT processing on the N number of time signal components and outputs N number of sub-carrier components. A channel estimation section (not illustrated) performs a known channel estimation operation and estimates channel coefficients of each sub-carrier, and generates a channel compensation value, and a channel compensation section 16 multiplies N number of FFT processing results by the channel compensation value so as to decrease the influence of channel distortion. Finally, a P/S converter 17 outputs N number of sub-carrier components after channel compensation is performed, sequentially in serial, a demodulation section 18 demodulates the input signal using BPSK, QPSK or 16-QAM, for example, and a decoding section 19 decodes and outputs the input data after deinterleave.